(1) Field of the Invention
The present invention relates to a broadcast system, and more particularly to a technique for allocating hardware resources to processings such as editing and broadcasting in a broadcast system where material data is written to a randomly accessible recording medium, edited, and broadcasted.
(2) Description of the Prior Art
A nonlinear broadcast system has increasingly been employed as a broadcast system for programs in recent years. In the nonlinear broadcast system, material data such as video that makes up the contents of broadcast programs is stored in a randomly accessible recording medium such as a hard disc, instead of a linear access device such as a video tape recorder (VTR) that does not allow an immediate access to specific data, the programs are edited quickly using a so-called nonlinear editing device, and the edited programs are broadcasted. The nonlinear broadcast system is particularly effective in editing and broadcasting up-to-the-minute news programs and sports relay programs.
In the nonlinear broadcast system, material data needs to be transferred from a hard disc or the like at a fixed transfer rate for broadcast. Otherwise, broadcast accidents such as frame-drop may happen.
The hard disc or the like is accessed for various purposes as follows. It may be accessed to store material data that has been collected for programs, to manipulate once stored material data, and to read material data for broadcast. To prevent the broadcast accidents from happening, therefore, bandwidth management relating to such accesses to the hard disc or the like needs to be performed.
In the nonlinear broadcast system capable of transmitting two sets of video data in a mixed state for realizing a so-called picture-in-picture function and a function of switching videos seamlessly, the two sets of video data that have been compressed and respectively stored in hard discs or the like are read out in parallel, transferred to CODECs (coder-decoder) where they are decompressed, and transmitted in a mixed state for broadcast.
To prevent the broadcast accidents from happening in such a nonlinear broadcast system, an enough bandwidth for transferring the two sets of video data from the hard discs or the like to the CODECs needs to be secured. Suppose that a bandwidth of 60 Mbps is required for reproducing each set of video data in real time. To broadcast a program, data transfer from the hard discs or the like needs to be performed with securing a bandwidth of 120 Mbps.
As an example of a conventional nonlinear broadcast system in which the hardware resource management is performed, Japanese Laid-Open Patent Application No. 11-261510 discloses the following nonlinear broadcast system. This nonlinear broadcast system features in its exclusive control structure where a broadcast device reserved by one user from a certain terminal cannot be used by the other terminals.
The structure of this conventional nonlinear broadcast system can be modified to perform the bandwidth management, by comparing the above broadcast device to a bandwidth utilized for a certain amount of data for accessing the hard disc or the like. If the user sets in advance to secure a fixed bandwidth of 120 Mbps for the two sets of video data for broadcasting the above program, data transfer that is free from the broadcast accidents can be realized. In this case, a bandwidth remaining after the bandwidth of 120 Mbps has been secured can be allocated to data transfer with less urgency such as writing material data to the hard disc or the like, or accessing the hard disc or the like for manipulating and editing the written material data.
However, even in the nonlinear broadcast system capable of transmitting two sets of video data in a mixed state, two sets of video data are not always required at one time, but at least one set of video data is always transmitted. Each set of video data is transmitted according to a video reproduction schedule determined in advance in a program editing procedure or the like, where transmission of two sets of video data at one time is scheduled at the maximum.
If an enough bandwidth to transfer video data from the hard disc or the like for broadcast is always secured in advance to prevent the broadcast accidents, that is to say, if an enough bandwidth to reproduce two sets of video data in real time is secured in advance, the problem often occurs as only a portion of the secured bandwidth is actually utilized. Since a relatively wide bandwidth is required for transferring video data, allowing such a bandwidth that is secured but not utilized leads to a drastic decrease in the utilization efficiency of hardware resources.